1. Field of Invention
The present invention relates to diagnostic apparatus and techniques for diagnosing and predicting failure in industrial machinery and, more particularly, to methods and apparatus for diagnosing the condition of rotating electrical and other machinery such as motors, generators, and gears wherein the diagnostics are integrated within the motor, generator, gear or other device.
2. Description of the Prior Art
A number of motor diagnostic methods and apparatus have been proposed in both the laboratory setting and elsewhere. U.S. Pat. No. 5,488,281 to Unsworth, et al. teaches a method and apparatus for predicting motor winding failure using zero crossing times. In that system, a motor controller is utilized which provides stator winding currents at a frequency of X cycles per second whereby the zero crossing times may be controlled and observed. In order to detect the zero crossing times and thus predict motor failure, the control system of the Unsworth, et al. apparatus alters the RMS supply line current by controlling the period of a notch introduced into the supply voltage each time the associated line current becomes zero. Thus, during the duration of the notch, a thyristor pair disposed in series with the motor lead wires operate as an open circuit. In that manner, instead of observing the sinusoidal supply voltage at the motor terminals, an internally generated motor back EMF voltage may be observed by the controller. Thus, in the Unsworth, et al. system, active motor control must be interrupted in order to detect and predict motor winding failures. Further, while the active motor control is interrupted, additional active inputs or signals must be introduced into the motor control circuit in order to induce the creation of observable motor parameters necessary to predict or conclude motor winding failures.
Another method and apparatus for determining the mechanical performance of polyphase electric motor systems is described in U.S. Pat. No. 5,521,482 to Lang et al. There, a fairly complicated apparatus is connected to the power lead wires connecting the motor to a power source. A plurality of signal conditioners are provided in order to generate signal levels suitable for use by a set of analog digital converters whereby the conditioned analog signals are converted to a digital representation thereof. A multiplexer is interposed between a central computer and the set of analog to digital converters thereby relieving the computer of the task of simultaneously reading each of the digital signals as they are generated in parallel. The computer is in turn connected to a communications port, a keyboard, a memory, a display unit and a printer. Although the above system may provide a method and apparatus for determining the electrical and mechanical performance parameters of a polyphase electric motor system in a laboratory or the like, it is not well suited for real time diagnosis of a motor operating in an industrial application.
The present invention overcomes many of the problems of the present conventional monitoring apparatus and techniques by providing a method and apparatus well suited for diagnosing motor conditions in the field while the motor is in use in production or the like. The present apparatus provides an integrated motor and motor diagnostic tool capable of passive observation of the operating parameters in an unobtrusive manner and thus without interference to the process to which the motor is connected. Further, the present invention provides the capability of alerting an operator of various motor fault conditions as they occur and, in addition, to alerting the operator of less serious cautions regarding the operation of the motor as well.